Acid copper electroplating baths



United States Patent 21 Claims. hi. 2e4-s2 This invention relates to the production of level, full bright copper electrodeposits from acid full bright cop per electroplating baths. It more specifically relates to such an electroplating bath stable over long periods of non-Operation and to additives for such stabilization.

In copending application Serial No. 25,242, filed April 28, 1960, now Patent No. 3,923,152, it was disclosed that a substantial improvement of acid full brightening copper electroplating baths can be achieved if, in addition to the customary brightening chemicals, those N-alkyl or N- aryl derivatives of thiourea are used as leveling agents which contain at least one alkyl-bonded or aryl-bonded carbonyl group in the molecule. Of particular interest in this connection are those known brightening compounds which contain one or more carbon atoms in the molecule which are attached only to hetero atoms and comprise a short aliphatic radical which is attached to the carbon atom through a sulfur atom and carries a sulfonic acid group or another water-solubilizing group, such as those compounds which are described in the copending application.

The subject matter of the present invention is a further improvement of these baths with respect to their stability over long periods of standing without the passage of current therethrough. This improvement is achieved by using those leveling agents in the baths according to the copending application which represent analogous isothiourea carboxylic acids or their salts wherein the sulfur of the isothiourea group is inactivated by suitable substituents.

These isothiourea derivatives are obtained according to known methods, that is by reacting the thiourea derivatives described above with halogen compounds such as halogen alkyls, halogen cycloalkyls, halogen alkylaryls or also with their substitution products such as halogen carboxylic acids and halogen ketones.

Thus, the additive compounds have general structural formulas as follows:

and

wherein R R and R represent hydrogen, alkyl, aryl, carboXy-alkyl or carbOXy-aryl radicals wherein at least one radical from R through R is always one of the carboxy radicals, and R and R are radicals defined as below and n is the number 2.

For example, the following isothiourea derivatives which are substituted at the sulfur atom by an R radical which may be alkyl, alkenyl, aryl, alkylaryl, phenacyl, carboXyalkyl (such as HOOCCH carboalkoxy (such as 3,179,578 Patented Apr. 20, 1965 CH .O.CO-) and similar radicals are useful for the purpose of the present invention:

S-methyl-N-phenyl-N-carboXymethyl-isothiourea S-ethyl-N-phenyl-N'-carboXymethyl-isothiourea S-benZyl-N-phenyl-N'-carboxymethyl-isothiourea S-allyl-N-phenyl-N'-carboxymethyl-isothiourea S-phenacyl-N-phenyl-N'-carboxymethyl-isothiourea S-carboxymethyl-N-phenyl-N-carboxyme-thyl-isothiourea S-carbomethoxy-N-phenyl-N'-carboxymethyl-isothiourea S-carboethoxy-N-phenyl-N'-carboXymethyl-isothiourea S-carbobenzoxy-N-phenyl-N-carboXymethyl-isothiourea S-carbophenoxy-N-phenyl-N'-carboxymethyl-isothiourea The deactivation of the sulfur atom of the leveling compounds may also be achieved by linking two molecules of the isothiourea compound through the sulfur atoms by means of an R radical comprising of an alkylene radical, i.e., methylene groups, such as in the case of the reaction product formed by 2 mols of N-phenyl-N-carboXymethylthiourea and 1 mol of 1,2-dibromoethane..

As indicated in the copending application Serial No. 25,242, it is here also essential for the effectiveness of the compound that the isothiourea radical carries alkylor aryl-bonded carboxyl groups on the nitrogen atom.

The leveling concentration range of the compound in the copper electroplating baths is from 1 to 50 mg./1. In all other respects the baths are operated under the customary conditions of concentration and temperature. The process may be operated over a wide current density range of from 0.02 to 10 amperes per square decimeter.

The thiourea derivatives according to the present invention exhibit a good leveling effect primarily with those full brightening agents which contain one or more carbon atoms in the molecule, the carbon atoms being bonded only to hetero atoms, and which include a short aliphatic radical which is attached to the molecule through a sulfur atom, the aliphatic radical carrying a sulfonic acid group or another water solubilizing group. Examples of such full brightening agents are: N,N-pentamethylene-dithiocarbamic w-sodium-sulfonate N,N-dimethyl-dithiocarbamic acid-n-propylester-w-sodium sulfonate N,N-diethylamino-dithiocarbamic acid-S-propandiol-2,3

N-butyl-dithiocarbamic acid-N,S-bis-propanew-potassiumsulfonate Dithiocarbamic acid-S-methylester-N-ethyl-N-butyl-w-potassium sulfonate 1,3,5 triazine-2,4,6-trimercapto-2-hydroxy sodium-propionate 1,3,S-triazine-2,4,6-trimercapto-ethane-ammonium sulfonate N,Ndimethyl-dithiocarbamic acid-n-ethylester-w-sodium sulfonate N,N-diethyl-dithiocarbamic acid-n-propylester-w-sodium sulfonate Morpholino-dithiocarbonic acid-n-propylester-w-sodium sulfonate Morpholino-dithiocarbonic acid-n-hydroxypropylester-wsodium sulfonate acid-n-propylesterand other full brightening agents of similar structure as disclosed in United States Patent Nos. 2,849,351 and 2,849,352.

The concurrent use of the thiourea derivatives according to the invention with the above described full brightening agents may also be panticularly applied to the process for direct copper electroplating, in which lirmly adhering copper electroplates are applied to non-precious metals, such as iron, without preliminary copperplating in a cyanide bath; this method comprises subjecting the metal 3 objects to be copperplated to a preliminary treatment in an acid pickling bath modified with inhibitors having a high inhibiting eifect, and subsequently electroplating the pickled objects in an acid copper bath without an intermediate rinsing step.

In order to increase the ductility of the copper electroplates produced from the baths containing the above agents, it has further been found to be advantageous to add certain organic amino compounds which are free from carboxyl groups, such as 1,3-propylene-diamine, 1,3-bis- (diethylarnino)-propanol-2, N,N,N,N tetrabutyl 1,3- diamonopropanol 2, N,N,N',N tetraethyl-1,3-diarnonopropanol-2 or also their sulfuric acid or sulfonic acid ester derivatives which contain one or more sulfonic acid groups or sulfonic acid ester groups. Other suitable agents for increasing the ductility are halogen-containing tertiary amino compounds free from carboxyl groups, such as 2-diethylamino 3 chloropropanol 2, or the quaternary rearrangement products formed from these compounds which contain the halogen in ionogenic linkage. Such compounds are disclosed in United States patents, Serial Nos. 735,360 and 2,842,488.

The following specific examples are given to illustrate my invention and to enable persons skilled in the art to better understand and practice the invention and are not intended to be limitative.

Example I An acid copper electroplating bath containing 200 gm./l. of CuSO .5H O, 60 gm./l. of concentrated sulfuric acid and as brightening agent 0.03-0.1 gm./l. of morpholino-dithiocarbonic acid-n-ethylester-w-sodium sulfonate as well as 0.25 gm./l. of N,N,N',N'-tetrabutyl-1,3-diaminopropanol-(2) and 2.5 grn./l. of the addition product of dodecyl alcohol and 8 mols of ethylene oxide, was modified with 0.001-0005 gm./l. of the sodium salt of S-allyl-N-phenyl-N'-carboxymethyl-isothiourea, obtained by reacting 1 mol N-phenyl-N-carboxymethyl-thiourea with 1 mol of allyl chloride. Full bright, level copper electrodeposits were obtained in a current density range of 0.57 amp/dm. at a temperature between 20 and 35 C. on unpolished brass sheets. Depressions of about 7 m in depth were smoothed out with copper deposits of to ITl/L by means of this electroplating bath. Without the addition of the isothiourea derivative, the copper electrodeposits were full bright but they were not level.

The preparation of the S-allyl-N-phenyl-N-carboxyrnethyl-isothiourea was effected as follows. 105 gm. of N-phenyl-N-carboxymethyl-thiourea and 76.5 gm. of allyl chloride were dissolved in 300 cc. of ethanol and the solution was boiled under reflux for four hours. After a short period of time the separation of the reaction product in crystalline form took place. After completion of the reaction the crystals were separated, washed and dried. 68 gm. of S-allyl-N-phenyl-N-carboxymethyl-isothiourea was obtained, which corresponded to about 47% of the theoretical yield. For transformation to the sodium salt, which was employed in the electroplating baths of the present invention, the free acid obtained above was dissolved in a dilute alkali metal solution which contained the stoichiometric amount of sodium hydroxide.

Example 11 A copper electroplating bath as in Example I was used, except that in place of the isothiourea derivative 0.002- 0009 gm./l. of the sodium salt of S-benZyl-N-phenyl-N- carboxymethyl-isothiourea was used as the leveling agent; the sodium salt was obtained by reacting 1 mol of N- phenyl-N-carboxyrnethyl-thiourea with 1 mol of benzyl chloride. This bath also produced leveling and mirror brightening effects.

Example III An acid copper electroplating bath as described in Example I was modified with 0.0010.01 gm./l. of the sodium salt of S-phenacyl-N-phenyl-N'-carboxymethylisothiourea, obtained by reacting 1 mol of N-phenyl-Y- carboxymethyl-thiourea with 1 mol of phenacyl chloride, as the leveling agent. The bath produced satisfactory level and mirror bright copper electroplates.

Example 1V An acid copper electroplating bath as described in Example I was modified with 0002-0006 gm./l. of the disodium salt of S-carboxymethyl-N-phenyl-N-carboxymethyl-isothiourea, obtained by reacting 1 mol of N- phenyl-N-carboxymethyl-thiourea with 1 mol of chloroacetic acid. The bath produced satisfactory level and full bright copper electroplates.

Example V An acid copper electroplating bath as described in Example I was modified with 0002-0017 gm./l. of the disodium salt of S,S'-ethylene-bis-N-phenyl-N'-carboxyrnethyl-isothiourea, obtained by reacting 2 mols of N- phenyl N carboxymethyl thiourea with 1 mol of 1,2- bromoethane. The bath produced level and full bright copper electroplates.

For preparation of the S,S-ethylene-bis-N-phenyl-N- carboxymethyl-isothiourea, gm. of N-phenyl-N'-carboxymethyl-thiourea and 94 gm. of 1,2-dibrornoethane were dissolved in 300 cc. of ethanol and the solution was boiled under reflux for six hours. The progress of the reaction was recognizable by the separation of the crystalline reaction product. After completion of the reaction the crystals were separated, washed and dried. The yield of 8,8 ethylene-bis-N-phenyl-N'-carboxymethyl-isothiourea was 74.2 gm. and thus corresponded to about 70% of the theoretical yield. For preparation of the sodium salt, which was employed in the electroplating bath according to the invention, the free acid obtained above was dissolved in a dilute alkali solution which contained the stoichiometric amount of sodium hydroxide.

While I have set forth certain specific examples and preferred modes of practice of my invention, it will be understood that the invention is not limited thereto, and that various changes and modifications may be made in my invention without departing from the spirit of the disclosure or the scope of the appended claims.

This application is a continuation-in-part of my copending application Serial No. 25,242, new Patent No. 3,023,152.

I claim:

1. A process for producing a smooth, bright copper electroplate on a rough surface metal base from acidic copperplating baths containing a brightening agent which comrpises adding to said bath as a smoothing agent a derivataive of isothiourea having a structural formula selected from the group consisting of:

wherein R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboxy-alkyl and carboxy-aryl radicals, at least one of R through R, being selected from the group consisting of earboxy-alkyl and carboxy-aryl radicals, R is a radical selected from the group consisting of alkyl, alkenyl, aryl, alkylaryl, phenacyl, carboxyalkyl and carboalkoxy radicals, R is an alkylene radical, and n is the number 2, said smoothing agent being added in sufiicient amount to effect said smoothing of the copper plate.

2. A process for producing a smooth, bright copper electroplate on a rough surface metal base from acidic copperplating baths containing a sulfonic acid brightening agent which comprises adding to said bath as a smoothing agent a derivative of isothiourea having a structural formula selected from the group consisting of:

wherein R R and R are selected vfrom the group consisting of hydrogen, alkyl, aryl, carboxy-alkyl and carboxy-aryl radicals, at least one of R through R being selected from the group consisting of carboxy-alkyl and carboXy-aryl radicals, R is a radical selected from the group consisting of alkyl, alkenyl, aryl, alkylaryl, phenacyl, carboxyalkyl and carboalkoxy radicals, R is an alkylene radical, and n is the number 2, said smoothing agent being added in suflicient amount to effect said smoothing of the copper plate.

3. The process of claim 2 wherein, in addition, the baths contain as ductility agents amino-compounds free from carboxyl groups, and sulfonic acid and sulfuric acid ester derivatives thereof. 7

4. The process of claim 2 wherein, in addition, the baths contain as ductility agents compounds selected from the group consisting of halogen-containing tertiary aminocompounds tree from carboxyl groups and quaternary rearrangement products thereof in which the halogen is present in ionogenic linkage.

5. The process of claim 2 wherein the amount of smoothing agent added is from 1 to 50 mg/l.

6. A process for producing a smooth, bright copper electroplate on a rough surface metal base from acidic copper plating baths containing a brightening agent having a carbon atom linked exclusively to heteroatoms, said carbon atom being further linked through a sulfur atom to a lower aliphatic chain which carries a water sol-ubilizing radical which comprises adding to said bath a derivative of isothiourea as a smoothing agent having a structural formula selected from the group consisting of and wherein R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboXy-alkyl and car- 'boXy-aryl radicals, at least one of R through R being selected from the group consisting of carboxy-alkyl and carboxy-aryl radicals, R is a radical selected from the group consisting of alkyl, alkenyl, aryl, alkylaryl, phenacyl, carboxyalkyl and carboalkoxy radicals, R is an alkylene radical, and n is the number 2, said smoothing agent being added in sufficient amount to effect said smoothing of the copper plate.

7. The process of claim 6 wherein the water solubilizing radical is a sulfonic acid radical.

8. The process of claim 6 wherein the brightening agent is morpholino-dithiocarbonic acid-n-ethylester-w-sodium sulfonate.

9. An electroplating bath for producing smooth, bright electrodeposits of copper on rough surface metal bases comprising an aqueous acid solution of an inorganic salt of copper, a brightening agent and as a smoothing agent a derivative of isothiourea having a structural formula selected from the group consisting of:

wherein R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboxy-alkyl and carboxy-aryl radicals, at least one of R through R being selected from the group consisting of canboXy-al'kyl and carboxy-aryl radicals, R is a radical selected from the group consisting of alkyl, alkenyl, aryl, alkyl-aryl, phenacyl, carboxyalkyl and carboalkoxy radicals, R is an alkylene radical, and n is the number 2, said smoothing agent being present in suificient amount to effect said smoothing of the electrodeposit.

10. An electroplating bath for producing smooth, bright electrodeposits of copper on a rough surface metal base comprising an aqueous acid solution of an inorganic salt of copper, a sulfonic acid brightening agent and as a smoothing agent a derivative of isothiourea having a structural formula selected from the group consisting of:

wherein R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboxy-alkyl and carboxy-aryl radicals, at least one of R through R being selected from the group consisting of carboxy-alkyl and carboxy-aryl radicals, R is a radical selected from the group consisting of alkyl, alkenyl, aryl, alkylaryl, phenacyl, carboxyalkyl and carboalkoxy radicals, R is an alkylene radical, and n is the number 2, said smoothing agent being present in sufiicient amount to eifect said smoothing of the electrodeposit.

11. The bath of claim 10 wherein, in addition, the baths contain as ductility agents amino-compounds free from carboxyl groups, and sulfonic acid and sulfuric acid ester derivatives thereof.

12. The bath of claim 10, wherein, in addition, the baths contain as ductility agents compounds selected from the group consisting of halogen-containing tertiary amino compounds free from carboxyl groups and quaternary rearrangement products thereof in which the halogen is present in ionogenic linkage.

13. The bath of claim 10 wherein the thiourea derivative is the sodium salt of S-allyl-N-phenyl-N'-carboxymethyl-isothiourea.

14. The bath of claim 10 wherein the thiourea derivative is the sodium salt of S-benzyl-N-phenyl-N'-carboxyinethyl-isothiourea.

15. The bath of claim 10 wherein the thiourea derivative is the sodium salt of S-phenacyl-N-phenyl-N'-carboxy-methyl-isothiourea.

16. The bath of claim 10 wherein the thiourea derivative is the disodium salt of S-carboxymethyl-N-phenyl- N'-carboxymethyl-isothiourea.

17. The bath of claim 10 wherein the thiourea derivative is the disodium salt of S,S-ethylene-bis-N-phenyl-N'- carboXymethyl-isothiourea.

18. The bath of claim 10 wherein the amount of smoothing agent added is from 1 to 50 mg/l.

19. An electroplating bath for producing smooth, bright electrodeposits of copper on a rough surface metal base comprising an aqueous acid solution of an inorganic salt of copper, a brightening agent having a carbon atom linked exclusively to heteroatoms, said carbon atom being further linked through a sulfur atom to a lower aliphatic chain which carriesa water solubilizing radical, and as a smoothing agent a derivative of isothioure-a having a structural formula selected from the group consisting of:

wherein R R and R are selected from the group consisting of hydrogen, alkyl, aryl, carboXy-alkyl and carboXy-aryl radicals, at least one of R through R being selected from the group consisting of carboXy-alkyl and carboxy-aryl radicals, R is a radical selected from the group consisting of alkyl, alkenyl, aryl, alkylaryl, phenacyl, carboxyalkyl and carboalkoxy radicals, R is an alkylene radical, and n is the number 2, said smoothing agent being present in sufficient amount to effect said smoothing of the eleetrodeposit.

20. The bath of claim 19 wherein the water solubilizing radical is a sulfonic acid radical.

21. The bath of claim 19 wherein the brightening agent is morpholino-dithiocarbonic acid-n-ethylester-w-sodium sulfonate.

References Cited by the Examiner UNITED STATES PATENTS 3,000,800 9/61 Strauss et a1. 204-52 3,023,152 2/62 Strauss et a1. 204-52 JOHN H. MACK, Primary Examiner.

MURRAY TILLMAN, Examiner. 

1. A PROCESS FOR PRODUCING A SMOOTH, BRIGHT COPPER ELECTROPLATE ON A ROUGH SURFACE METAL BASE FROM ACIDIC COPPERPLATING BATHS CONTAINING A BRIGHTENING AGENT WHICH COMPRISES ADDING TO SAID BATH AS A SMOOTHING AGENT A DERIVATIVE OF ISOTHIOUREA HAVING A STRUCTURAL FORMULA SELECTED FROM THE GROUP CONSISTING OF: 